Heat-hardenable paint compositions

ABSTRACT

The invention relates to heat-hardenable paint composition which contains (A) vinyl based copolymer of hydroxyl group value from 20 to 200 mg KOH/g, being a copolymer of from 5 to 70 wt % hydroxyl group containing a particularly defined vinyl based monomer and from 95 to 30 wt % other vinyl based monomer (a-2), and (B), a particularly defined 1,3,5-triazine-2,4,6-triscarbamic acid ester, or an oligomer thereof, in which the mol ratio of hydroxyl groups originating from the aforementioned (A) component: NHCOOR groups originating from the aforementioned (B) component in the composition is from 1:3 to 3:1.

FIELD OF THE INVENTION

This invention concerns heat-hardenable paint compositions and, moreprecisely, it concerns heat-hardenable paint compositions which aresuitable as top-coat paints for use on automobiles.

BACKGROUND OF THE INVENTION

In recent years, the deterioration in the external appearance of paintfilms due to chemical and physical causes, such as etching by acid rainand scratching during cleaning of the paint film for example, has beenseen as a problem in the field of automobile paints, for example.

Acrylic-melamine based top-coat paint compositions in whichε-caprolactone modified acrylic resin and specified low molecular weightpolyols are used conjointly in the essential structural material of thepaint film and in which soft segments are introduced by hardening withan alkoxy monomeric melamine (for example, Japanese Patent Kokai64-66274, (1989)) have been suggested as a means of resolving theseproblems.

However, the abovementioned paint compositions are such that the paintfilm forming resin itself is modified with ε-caprolactone and so thepaint film is softened and the scratch resistance can be improved, butthe acid resistance is inadequate because alkoxy monomeric melamine isused, and this is inappropriate for dealing with severe acid rain in thefuture.

Furthermore, top-coat paint compositions which have ε-caprolactonemodified acrylic resin and non-yellowing type blocked polyisocyanatecompounds as essential components (for example, Japanese Patent KokaiH2-305873 (1990)) have also been suggested with the same end in view.

However, although both scratching resistance and acid resistance areimproved with the abovementioned compositions, a blocked isocyanatecompound is used for the crosslinking agent and so the paint film infact liable to yellowing even though it is said to be a non-yellowingtype, and in practice the non-yellowing properties are inadequate.

On the other hand, hardenable compositions which contain poly-functionalhydroxyl group containing materials, 1,3,5-triazine-2,4,6-tris-carbamicacid esters, and acid hardening catalysts have been disclosed inJapanese Patent Kokai H6-228305 (1994), and it is stated that paintfilms which release little formaldehyde and which have excellent acidresistance are obtained.

However, these compositions are inadequate in terms of weatherresistance and thermal stability, and paint film defects such ascracking and loss of gloss due to exposure to ultraviolet radiation areliable to occur with paint films which have been formed under hardeningconditions of temperature above 140° C. in particular.

The aim of this invention is to provide heat-hardenable paintcompositions with which paint films which have excellent scratchingresistance, acid resistance, yellowing resistance and weather resistancecan be formed in order to resolve the problems outlined above.

SUMMARY OF THE INVENTION

The present invention provides the following heat-hardenable paintcompositions:

(1) Heat-hardenable paint composition which contains (A) vinyl basedcopolymer of hydroxyl group value from 20 to 200 mg KOH/g, being acopolymer of from 5 to 70 wt % hydroxyl group containing vinyl basedmonomer (a-1) which can be represented by general formula (1) which isindicated below and from 95 to 30 wt % other vinyl based monomer (a-2),and (B) 1,3,5-triazine-2,4,6-triscarbamic acid ester which can berepresented by the general formula (2) which is indicated below, or anoligomer thereof, characterized in that the mol ratio of hydroxyl groupsoriginating from the aforementioned (A) component: NHCOOR groupsoriginating from the aforementioned (B) component in the composition isfrom 1:3 to 3:1.

General Formula (1) ##STR1## (In this formula, X¹, X² and X³ eachindependently represent a hydrogen atom or a methyl group. Moreover j isan integer of value from 0 to 2, m is an integer of value from 3 to 5,and n is an integer of value from 0 to 5. However, j and n cannot bothbe 0.)

General Formula (2)

    C.sub.3 N.sub.3 (NHCOOR).sub.3                             (2)

(In this formula, R represents an alkyl group which has from 1 to 20carbon atoms, an aryl group which has from 6 to 20 carbon atoms or anaralkyl group which has from 7 to 20 carbon atoms, and these groups maybe the same or different.)

(2) Heat-hardenable paint composition which contains (C) vinyl basedcopolymer of hydroxyl group value from 20 to 200 mg KOH/g, being acopolymer which contains from 5 to 70 wt % structural units (c-1) whichcan be represented by general formula (3) which is indicated below andfrom 95 to 30 wt % other structural units (c-2) derived from vinyl basedmonomer, and (B) 1,3,5-triazine-2,4,6-triscarbamic acid ester which canbe represented by the general formula (2) which is indicated below, oran oligomer thereof, characterized in that the mol ratio of hydroxylgroups originating from the aforementioned (C) component: NHCOOR groupsoriginating from the aforementioned (B) component in the composition isfrom 1:3 to 3:1.

General Formula (3) ##STR2## (In this formula, X¹, X² and X³ eachindependently represent a hydrogen atom or a methyl group. Moreover j isan integer of value from 0 to 2, m is an integer of value from 3 to 5,and n is an integer of value from 0 to 5. However, j and n cannot bothbe 0.)

General Formula (2)

    C.sub.3 N.sub.3 (NHCOOR).sub.3                             (2)

(In this formula, R represents an alkyl group which has from 1 to 20carbon atoms, an aryl group which has from 6 to 20 carbon atoms or anaralkyl group which has from 7 to 20 carbon atoms, and these groups maybe the same or different.)

In this invention, the term "(meth)acrylic" signifies "acrylic" and/or"methacrylic".

X¹, X² and X³ in the aforementioned general formula (1) or (3) arehydrogen atoms or methyl groups, and they may be the same or different.Furthermore, j is an integer of value from 0 to 2, m is an integer ofvalue from 3 to 5 and n is an integer of value from 0 to 5. However, jand n cannot both be 0 at the same time. If n exceeds 5 then the solventresistance of the paint film obtained is reduced and so this isundesirable.

DETAILED DESCRIPTION OF THE INVENTION

Actual examples of the aforementioned hydroxyl group containing monomerswhich can be represented by general formula (1) include hydroxypropyl(meth)acrylate and hydroxybutyl (meth)acrylate, for example, as monomersin which n is 0, and the lactone modified vinyl based monomers where alactone has been added to a hydroxyl group containing vinyl basedmonomer, such as hydroxyethyl (meth)acrylate, hydroxypropyl(meth)acrylate or hydroxybutyl (meth)acrylate for example, as monomersin which n is from 1 to 5.

ε-Caprolactone, β-methyl-δ-valerolactone, γ-valerolactone,δ-valerolactone, δ-caprolactone, γ-caprolactone, β-propiolactone andγ-butyrolactone, for example, can be cited for the abovementionedlactones.

The aforementioned lactone modified vinyl based monomers can bemanufactured by adding from 1 to 5 mol of the abovementioned lactones to1 mol of the aforementioned hydroxyl group containing vinyl basedmonomers. If, in this case, the lactones are added in an amountexceeding 5 mol then the solvent resistance after paint film formationis poor and this is undesirable. The method whereby ε-caprolactone isreacted in the presence of a catalyst with a hydroxy group containingvinyl based monomer, as disclosed in Japanese Patent Kokai 63-118317(1988) for example, and other known methods, can be adopted for themethod of addition.

Commercial products can be used for the aforementioned hydroxyl groupcontaining vinyl based monomer (a-1) which can be represented by thegeneral formula (1) and, for example, "Praxel" manufactured by theDaiseru Kagaku Co. or "TONE" manufactured by the Union Carbide Co. (bothtrade names) can be used as lactone modified vinyl based monomers.

A single type of hydroxyl group containing vinyl based monomer (a-1) canbe used alone, or two or more types can be used in combination.

C₁₋₁₈ alkyl or cycloalkyl esters of (meth)acrylic acid, such as methyl(meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl(meth)acrylate, i-butyl (meth)acrylate, t-butyl (meth)acrylate,2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate, n-octyl(meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate andstearyl (meth)acrylate; and also styrene, styrene derivatives,acrylonitrile, acrylamide, vinyltoluene, vinyl acetate, glycidyl(meth)acrylate, acrylic acid, methacrylic acid and 2-hydroxyethyl(meth)acrylate, for example, can be cited as other vinyl based monomers(a-2) which can be copolymerized with the hydroxyl group containingvinyl based monomer (a-1).

One of the other vinyl based monomers (a-2) can be used alone, or two ormore types can be used in combination.

In this invention, the vinyl based copolymer which is used for component(A) is a copolymer of from 5 to 70 wt %, and preferably from 10 to 60 wt%, hydroxy group containing vinyl based monomer (a-1) which can berepresented by the aforementioned general formula (1) and from 95 to 30wt %, and preferably from 90 to 40 wt %, of the other vinyl basedmonomer (a-2). In those cases where the proportion of hydroxyl groupcontaining vinyl based monomer (a-1) is less than 5 wt % the scratchingresistance of the paint film is inadequate, and if the amount exceeds 70wt % then the hardness of the paint film is inadequate and the solventresistance is reduced and so this is undesirable.

The hydroxyl group value of the vinyl based copolymer (A) used in theinvention is from 20 to 200 mg KOH/g, and preferably from 40 to 180 mgKOH/g. In those cases where the hydroxyl group value is less than 20 mgKOH/g the solvent resistance of the hardened paint film is reduced, andin those cases where it exceeds 200 mg KOH/g the flex resistance of thehardened paint film is reduced and so this is undesirable.

The vinyl based copolymer (A) is obtained by copolymerizing theaforementioned hydroxyl group containing vinyl based monomer (a-1) andthe other vinyl based monomer (a-2). Known methods can be used for thepolymerization, and polymerization methods such as solutionpolymerization, non-aqueous dispersion polymerization and bulkpolymerization, for example, can be adopted, and solution polymerizationis especially desirable.

In this invention, the vinyl based copolymer which is used as the (C)component is a copolymer which contains from 5 to 70 wt %, andpreferably from 10 to 60 wt %, of structural units (c-1) which can berepresented by the aforementioned general formula (3) and from 95 to 30wt %, and preferably from 90 to 40 wt %, of other structural units (c-2)which are derived from vinyl based monomer. In those cases where theproportion of structural units (c-1) is less than 5 wt % the scratchingresistance of the paint film is inadequate, and if it exceeds 70 wt %then the hardness of the paint film is inadequate and the solventresistance is reduced and so this is undesirable.

Furthermore, the hydroxyl group value of the vinyl based copolymer (C)used in the invention is from 20 to 200 mg KOH/g, and preferably from 40to 180 mg KOH/g. In those cases where the hydroxyl group value is lessthan 20 mg KOH/g the solvent resistance of the hardened paint film isreduced, and in those cases where it exceeds 200 mg KOH/g the flexresistance of the hardened paint film is reduced, and so this isundesirable.

The structural units (c-1) represented by the aforementioned generalformula (3) are structural units derived from hydroxyl group containingvinyl based monomers (a-1) which can be represented by theaforementioned general formula (1), and they are also structural unitswhich are derived by adding lactones to the vinyl based monomers whichcontain hydroxyl groups as will be described hereinafter. Furthermore,the structural units (c-2) are structural units derived from theaforementioned other vinyl based monomers (a-2), and they have astructure which can be represented by general formula (4) below.

General Formula 4 ##STR3## (In this formula, R¹ is a hydrogen atom or amethyl group, and R² is the residual group of the other vinyl basedmonomer (a-2).)

The vinyl based copolymer (C), as in the case of the vinyl basedcopolymer (A), is obtained by copolymerizing the aforementioned hydroxylgroup containing vinyl based monomer (a-1) and the other vinyl basedmonomer (a-2). Furthermore, it can be obtained by adding theaforementioned lactones to the hydroxyl groups of the copolymer afterobtaining the vinyl based copolymer which contains hydroxyl groups bycopolymerizing a vinyl based monomer which contains hydroxyl group, suchas hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate orhydroxyethyl (meth)acrylate for example, and the aforementioned othervinyl based monomer (a-2).

The known methods can be adopted for the addition of lactones and, forexample, the method in which the aforementioned lactones are drippedinto and mixed with a solution of the copolymer in the presence of anorganometallic compound catalyst, such as dibutyltin dilaurate ortetrabutyltitanate for example, or an acid such as carboxylic acid,phosphoric acid or sulfonic acid, and a ring-opening addition reactioncarried out at a temperature of from 80 to 160° C. can be used.

The (B) component used in the invention is a crosslinking component, anda 1,3,5-triazine-2,4,6-triscarbamic acid ester which can be representedby the aforementioned general formula (2), an oligomer thereof, or amixture of these can be used.

Alkyl groups which have from 1 to 20 carbon atoms, such as the methyl,ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl,pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl,tetradecyl, heptadecyl and eicosyl groups; aryl groups which have from 6to 20 carbon atoms, such as the phenyl, tolyl, naphthyl and anthrylgroups and the substituted aryl groups where alkyl group have beensubstituted on the aromatic rings of these groups; and aralkyl groupswhich have from 7 to 20 carbon atoms such as the benzyl and phenethylgroups and the substituted aralkyl groups where alkyl groups have beensubstituted in the aromatic rings of these groups, can be cited asactual examples of R in the aforementioned general formula (2).

The R groups in the aforementioned general formula (2) may be the sameor different.

From among the 1,3,5-triazine-2,4,6-triscarbamic acid esters which canbe represented by the aforementioned general formula (2), the compoundsin which R is an alkyl group which has from 1 to 8 carbon atoms arepreferred, and 2,4,6-tris(methoxycarbonylamino)-1,3,5-triazine which canbe represented by C₃ N₃ (NHCOOCH₃)₃,2,4,6-tris(butoxycarbonylamino)-1,3,5-triazine which can be representedby C₃ N₃ (NHCOOC₄ H₉)₃, and mixtures of these, are especially desirable.

Furthermore, oligomers where compounds which can be represented bygeneral formula (2) have been partially condensed with diols can also beused for the (B) component. Examples of the diols which can be used hereinclude ethylene glycol, diethylene glycol, propylene glycol,propanediol, butanediol, pentanediol, hexanediol and neopentyl glycol.

The compounding proportions of the (A) component (or (C) component) andthe (B) component are such that the mol ratio of hydroxyl groupsoriginating from the (A) component (or (C) component): NHCOOR groupsoriginating from the (B) component is from 1:3 to 3:1, and preferablyfrom 1:2 to 2:1.

The solvent resistance of the hardened paint film is reduced in thosecases where the abovementioned mol ratio is below 1:3 and so this isundesirable, while in those cases where the mol ratio exceeds 3:1 thewater resistance of the hardened paint film is reduced and so this isundesirable.

The (A) or (C) component hydroxyl group containing vinyl based copolymerhas the hydroxyl groups arranged in locations displaced from the mainchain by soft segments and so crosslinking bonds which are flexible areformed by crosslinking such a copolymer with a carbamic acid ester basedhardening agent which can be represented by the aforementioned generalformula (2) which is the (B) component. Consequently, the hardened paintfilms which are obtained have excellent scratching resistance.Furthermore, the crosslinking bonds which are formed with a carbamicacid ester based hardening agent are chemically stable and so they haveexcellent acid resistance and weather resistance. Moreover, the carbamicacid ester (B) does not cause yellowing of the paint film.

Other hardening components which can react with hydroxyl groups, as wellas the (B) component, can also be compounded as auxiliary crosslinkingcomponents in a paint composition of this invention. Blocked isocyanateresin, amino resin, melamine resin, silanol resins and alkoxysilaneresins, for example, can be cited as other hardening agent componentswhich can react with hydroxyl groups. However, it is desirable forrealizing satisfactorily the effect of this invention that the otherhardening component is included in an amount of less than 20 wt % of thetotal resin solid fraction, and in those cases where blocked isocyanateresins are compounded as auxiliary crosslinking components in particularit is desirable that the amount should be less than 15 wt % inconsideration of the yellowing of the paint film.

Furthermore, hardening catalysts other than the abovementionedcomponents can be compounded in a paint composition of this invention inorder to obtain hardened paint films more efficiently. Examples ofhardening catalysts include tin based catalysts such as dibutyltindilaurate, dibutyltin diacetate and tin octanoate; sulfonic acid basedcatalysts such as p-toluenesulfonic acid, dodecylbenzenesulfonic acid,dinonylnaphthalenesulfonic acid and dinonylnaphthalenedisulfonic acid;and also phosphoric acid based catalysts and carboxylic acid basedcatalysts, and one type can be used alone or mixtures of two or moretypes can be used.

Moreover, the additives which are used conventionally in paints,including colorants such as pigments and dyes, pigment dispersants,viscosity adjusting agents, anti-run agents, leveling agents,anti-gelling agents, ultraviolet absorbers and radical scavengers, forexample, can also be added to a paint composition of this invention, asrequired, within ranges such that the purpose of the invention is notlost.

Paint compositions of this invention can be manufactured by mixing theaforementioned (A) and (B) components, or the (C) and (B) components,and the other components, as required.

The paint compositions of this invention can be compounded with coloredpigments, metallic pigments, dyes or physical pigments, for example, andused as colored paints (solid color finish) or metallic paints forexample. Furthermore, they can also be used as clear paints in whichlittle or no pigment is compounded.

No particular limitation is imposed upon the objects which can bepainted with a paint comprising a paint composition of this invention,and it is possible to paint metals, such as steel sheets and surfacetreated steel sheets, and plastics, for example, and they can be used topaint directly onto these materials or they can be painted as top-coatpaints onto painted surfaces where a primer or a primer/mid-coat painthas been applied to the material which is to be painted. In practicalterms, they can be used as top-coat paints for automobiles and othervehicles, buildings and structures for example.

A film thickness of some 10 to 60 μm as a dry film thickness ispreferred, and the preferred baking conditions for hardening the paintfilm are a temperature of from about 100° C. to about 180° C. and a timeof some 10 to 120 minutes.

Paints comprising a paint composition of this invention can be used forone-coat one-bake painting, two-coat one-bake painting, three-coattwo-bake painting or three-coat one-bake painting for example, and theycan be painted using the normal methods of painting, for example airspray painting, airless spray painting, electrodeposition painting ordip painting, to provide the aforementioned dry film thickness, and ahardened paint film can be formed under the aforementioned bakingconditions. In those cases where the paints comprising a paintcomposition of this invention are used as top coat clear paints, anytype of paint, such as a solvent based paint, a high-solid paint or awater based paint for example, can be used for the colored base coat.

The hydroxyl group containing vinyl based copolymers which are used forthe main resin in this invention have the hydroxyl groups arranged inlocations displaced from the main chain by soft segments and thecrosslinking bonds which are formed with the carbamic acid ester basedhardening agent are flexible and chemically stable. Moreover, thecarbamic acid esters represented by general formula (2) do not causeyellowing of the paint film.

The heat-hardenable paint composition of this invention containsspecified amounts of the abovementioned hydroxyl group containing vinylbased copolymers and hardening agents and so it is possible to formpaint films which have excellent scratching resistance, acid resistance,yellowing resistance and weather resistance.

The invention is described in more detail below by means of examples ofmanufacture, illustrative examples and comparative examples, but theinvention is not limited in any way by these examples.

Manufacture of Vinyl Based Copolymers EXAMPLE OF MANUFACTURE 1

Xylene (370 parts by weight) was introduced into a four-necked flaskwhich had been fitted with a thermometer, a stirrer, a reflux condenserand a dropping funnel and the temperature was raised to 140° C. Next, amixture of which the composition is indicated below was added dropwisefrom the dropping funnel at a constant rate over a period of 2 hours.After completing the drip feed, the mixture was maintained at the refluxtemperature for a period of 1 hour and then the contents of the flaskwere cooled to 100° C. Then, 2 parts by weight oftert-butylperoxy-2-ethylhexanoate and 10 parts by weight of xylene wereadded and, by maintaining at a temperature of 100° C., with stirring,for a period of 2 hours, the (A) component hydroxyl group containingvinyl based copolymer solution A-1 of residue on heating 60%, resinhydroxy group value 100 mg KOH/g and weight average molecular weight10,000 was obtained.

    ______________________________________                                        Praxel FM-1 *1      261    parts by weight                                      2-Ethylhexyl methacrylate 39 parts by weight                                  n-Butyl methacrylate 300 parts by weight                                      tert-Butyl peroxybenzoate 20 parts by weight                                ______________________________________                                         *1 Praxel FM1: Trade name of a compound of the aforementioned general         formula (1) in which X.sup.1 is a methyl group, X.sup.2 and X.sup.3 are       hydrogen atoms, j is 0, m is 5 and n is 1, manufactured by the Daiseru        Kagaku Co.                                                               

EXAMPLE OF MANUFACTURE 2

Xylene (370 parts by weight) was introduced into a four-necked flaskwhich had been fitted with a thermometer, a stirrer, a reflux condenserand a dropping funnel and the temperature was raised to 140° C. Next, amixture of which the composition is indicated below was added dropwisefrom the dropping funnel at a constant rate over a period of 2 hours.After completing the drip feed, the mixture was maintained at the refluxtemperature for a period of 1 hour and then the contents of the flaskwere cooled to 100° C. Then, 2 parts by weight oftert-butylperoxy-2-ethylhexanoate and 10 parts by weight of xylene wereadded and, by maintaining at a temperature of 100° C., with stirring,for a period of 2 hours, the (A) component hydroxyl group containingvinyl based copolymer solution A-2 of residue on heating 60%, resinhydroxy group value 150 mg KOH/g and weight average molecular weight10,000 was obtained.

    ______________________________________                                        4-Hydroxybutyl acrylate                                                                           232    parts by weight                                      2-Ethylhexyl methacrylate 240 parts by weight                                 n-Butyl methacrylate 128 parts by weight                                      tert-Butyl peroxybenzoate 20 parts by weight                                ______________________________________                                    

EXAMPLE OF MANUFACTURE 3

Xylene (370 parts by weight) was introduced into a four-necked flaskwhich had been fitted with a thermometer, a stirrer, a reflux condenserand a dropping funnel and the temperature was raised to 140° C. Next, amixture of which the composition is indicated below was added dropwisefrom the dropping funnel at a constant rate over a period of 2 hours.After completing the drip feed, the mixture was maintained at the refluxtemperature for a period of 1 hour and then the contents of the flaskwere cooled to 100° C. Then, 1 part by weight oftert-butylperoxy-2-ethylhexanoate and 10 parts by weight of xylene wereadded and it was maintained at a temperature of 100° C., with stirring,for a period of 2 hours.

    ______________________________________                                        2-Hydroxyethyl methacrylate                                                                       139    parts by weight                                      Methyl methacrylate 80 parts by weight                                        isobutyl methacrylate 15 parts by weight                                      tert-Butyl peroxybenzoate 5 parts by weight                                 ______________________________________                                    

Next, 3 parts by weight of dibutyltin dilaurate and 11 parts by weightof xylene were added, and then 366 parts by weight of ε-caprolactam wereadded dropwise from the dropping funnel at a constant rate over a periodof 1 hour. After the drip feed had been completed, the reaction wascontinued at a temperature of 100° C. and the reaction was completedwhen the residue on heating reached 60%, and the (C) component hydroxylgroup containing vinyl based copolymer solution C-1 of resin hydroxylgroup value was 100 mg KOH/g and weight average molecular weight 20,000was obtained.

EXAMPLE OF MANUFACTURE 4

Xylene (370 parts by weight) was introduced into a four-necked flaskwhich had been fitted with a thermometer, a stirrer, a reflux condenserand a dropping funnel and the temperature was raised to 140° C. Next, amixture of which the composition is indicated below was added dropwisefrom the dropping funnel at a constant rate over a period of 2 hours.After completing the drip feed, the mixture was maintained at the refluxtemperature for a period of 1 hour and then the contents of the flaskwere cooled to 100° C. Then, 2 parts by weight oftert-butylperoxy-2-ethylhexanoate and 10 parts by weight of xylene wereadded and, by maintaining at a temperature of 100° C., with stirring,for a period of 2 hours, the hydroxyl group containing vinyl basedcopolymer solution a-4 of residue on heating 60%, resin hydroxy groupvalue 100 mg KOH/g and weight average molecular weight 10,000 wasobtained.

    ______________________________________                                        2-Hydroxyethyl methacrylate                                                                       139    parts by weight                                      2-Ethylhexyl methacrylate 411 parts by weight                                 n-Butyl methacrylate 50 parts by weight                                       tert-Butyl peroxybenzoate 20 parts by weight                                ______________________________________                                    

Illustrative Examples 1 to 5

a) Preparation of Clear Paints

Clear paints of the compositions shown in Table 1 were prepared anddiluted to the painting viscosity (Ford Cup #4, 25 seconds at 20°) usinga thinner ["Sorbesso #100 (trade name, aromatic hydrocarbon of boilingpoint 150-170° C. manufactured by the Esso Co.)/n-butanol=8/2 by weight]and used to form the paint films indicated below.

b) Formation of Paint Films

Cationic electrodeposition paint ("Aqua No.4200", trade name,manufactured by the Nippon Yushi Co.) was electrodeposition painted ontozinc phosphate treated mild steel sheet to a dry film thickness of 20 μmand then baked at a temperature of 175° C. for 25 minutes, and then amid-coat paint ("Hiepico No.100 White", trade name, manufactured by theNippon Yushi Co.) was spray painted in such a way as to provide a dryfilm thickness of 40 μm and baked at 140° C. for 30 minutes and amid-coat painted sheet was obtained.

In Examples 1 to 4, a solvent type base-coat paint ("Belcoat No.6000White", trade name, manufactured by the Nippon Yushi Co.) was air spraypainted into this mid-coat painted sheet to a dry film thickness of 20μm and then set for 5 minutes at room temperature, and then each of theaforementioned clear paints prepared in a) was air spray painted in sucha way as to provide a dry film thickness of 40 μm and then baked at 140°C. for 30 minutes.

On the other hand, in Example 5 a water based base-coat paint (a whitebased paint prepared using titanium oxide for the pigment using the samemethod as that disclosed in Example 1 of Japanese Patent Kokai H8-10690(1996)) was air spray painted onto similar electrodeposition/mid-coatpainted sheet to that described above so as to provide a dry filmthickness of 20 μm and, after flashing for 10 minutes at 80° C., theaforementioned clear paints prepared in a) were air spray painted insuch a way as to provide a dry film thickness of 40 μm and baked at 140°C. for 30 minutes.

Moreover, specimens were obtained by the direct painting of the clearcoat paint onto "Hiepico No.100 Black" (trade name, manufactured by theNippon Yushi Co.) for the scratching resistance tests of Examples 1 to5.

On carrying out each of the tests shown in Table 3 with the sheetsobtained as samples, all of the examples shown in Table 3 exhibitedexcellent scratching resistance, acid resistance, yellowing resistanceand weather resistance.

Comparative Examples 1 and 2

a) Preparation of Clear Paints

The clear paints of the compositions shown in Table 2 were prepared anddiluted to the painting viscosity (Ford Cup #4, 25 seconds at 20°) usinga thinner ["Sorbesso #100 (trade name, aromatic hydrocarbon of boilingpoint 150-170° C., manufactured by the Esso Co.)/n-butanol=8/2 byweight] and used to form the paint films indicated below.

b) Formation of Paint Films

In the same way as in Examples 1 to 4, solvent type base-coat paint("Belcoat No.6000, White", trade name, manufactured by the Nippon YushiCo.) was air spray painted to provide a dry film thickness of 20 μm ontocationic electrodeposition/mid-coat painted sheet and, after setting for5 minutes at room temperature, each of the aforementioned clear paintsprepared in a) was air spray painted so as to provide a dry filmthickness of 40 μm and baked at 140° C. for 30 minutes.

The paint film performance was investigated using the specimensobtained. The results are shown in Table 3.

                  TABLE 1                                                         ______________________________________                                        (Amount Compounded, Units: Part by Weight)                                                 Example                                                                       1       2       3     4     5                                    ______________________________________                                        A-1 *1       44.2    74.9    --    --    74.9                                   A-2 *2 -- -- -- 79.6  --                                                      C-1 *3 -- -- 44.2  -- --                                                      a-4 *4 -- -- -- -- --                                                         B-1 *5 53.7  22.8  53.7  18.1  22.8                                           b-2 *6 -- -- -- -- --                                                         Tinuvin 384 *7 1.0 1.1 1.0 1.2 1.1                                            Tinuvin 292 *8 0.5 0.6 0.5 0.6 0.6                                            DBTDL *9 0.3 0.3 0.3 0.3 0.3                                                  BYK 306 *10 0.3 0.3 0.3 0.2 0.3                                               TOTAL 100.0  100.0  100.0  100.0  100.0                                       OH group: 1:2 1:1 1:2 2:1 1:1                                                 NHCOOR *11                                                                    Base-Coat ST ST ST ST WB                                                    ______________________________________                                         ST: Solvent Type, WB: Water Based                                        

                  TABLE 2                                                         ______________________________________                                        (Amount Compounded, Units: Part by weight)                                                     Comparative Example                                                           1         2                                                  ______________________________________                                        A-1 *1           --        65.0                                                 A-2 *2 -- --                                                                  C-1 *3 -- --                                                                  a-4 *4 74.9  --                                                               B-1 *5 22.8  --                                                               b-2 *6 -- 33.5                                                                Tinuvin 384 *7 1.1 0.7                                                        Tinuvin 292 *8 0.6 0.4                                                        DBTDL *9 0.3 0.3                                                              BYK 306 *10 0.3 0.1                                                           TOTAL 100.0  100.0                                                            OH group: NHCOOR *11 1:1                                                      Base-Coat Solvent Type Solvent Type                                         ______________________________________                                         Notes for Tables 1 and 2                                                      *1 A1: Vinyl based copolymer solution A1 of Example of Manufacture 1          *2 A2: Vinyl based copolymer solution A2 of Example of Manufacture 2          *3 C1: Vinyl based copolymer solution A3 of Example of Manufacture 3          *4 a4: Vinyl based copolymer solution a4 of Example of Manufacture 4          *5 B1: nButanol solution of 2,4,6tris(butoxycarbonylamino)-1,3,5-triazine     this compound has been disclosed in Japanese Pat. Kokai H6228305 (1994).      *6 b2: Blocked isocyanate (HDI) manufactured by the Sumitomo Bayer            Urethane Co., blocked isocyanate for which the isocyanate groups of           hexamethylenediisocyanate have been blocked with an oxime derivative,         Desmodure BL3175, manufactured by the Sumitomo Bayer Urethane Co., trade      name, NCO % = 11.1%, solid fraction 75%.                                      *7 Tinuvin 384: Trade name, manufactured by the Ciba Geigy Co., a             benzotriazole based ultraviolet absorber                                      *8 Tinuvin 292: Trade name, manufactured by the Ciba Geigy Co., a hindere     amine based radical scavenger.                                                *9 DBTDL: Dibutyltin dilaurate                                                *10 BYK 306: A leveling agent, BYK 306 manufactured by the Bikkemy Co.        (trade name)                                                                  *11 OH group: NHCOOR                                                     

This shows the mol ratio of hydroxyl groups originating from the (A)component: NHCOOR groups originating from the (B) component in the paintcomposition.

                  TABLE 3                                                         ______________________________________                                                                 Comparative                                            Examples Examples                                                                  1     2     3       4   5     1    2                                   ______________________________________                                        Scratching *1                                                                          ◯                                                                         ◯                                                                       ◯                                                                       ◯                                                                     ◯                                                                       X    ◯                       Resistance                                                                    Acid *2 ◯ ◯ ◯ ◯                                                         ◯ ◯                                                   ◯                       Resistance                                                                    Pencil *3 H H H H H-F H H                                                     Hardness                                                                      Yellowing *4 ◯ ◯ ◯ ◯                                                    ◯ ◯ X       Resistance                                                                    Accelerated *5 ◯ ◯ ◯ ◯                                                  ◯ X ◯       Weather                                                                       Resistance                                                                  ______________________________________                                         Notes for Table 3                                                             *1 Scratching Resistance: Muddy water (JIS Z8901-84, a mixture of type 8      dust/water/neutral detergent = 10/99/1 by weight) was coated with a brush     onto the sample and then the sample was washed with the washing wheel         brush in an automobile washer at 150 rpm for 10 seconds and rinsed with       running water. This operation was repeated twice and the extent of            scratching of the sample surface was observed visuals.                        ◯: Hardly any scratching to be seen                               Δ: Slight scratching was seen                                           X: Pronounced scratching was seen                                             *2 Acid Resistance: After placing 0.2 ml of 40 wt % aqueous sulfuric acid     solution in the form of a spot on the sample it was heated to 60°      C. for 15 minutes and then rinsed with water, and the extent of marking       was assessed visually.                                                        ◯: No abnormality                                                 X: Water mark present                                                         *3 Pencil Hardness: Pencil scratching tests were carried out in accordanc     with JIS K5400 ((1992) 8.4.2) in a constant temperature, constant humidit     room at 20° C. and 75% RH.                                             *4 Yellowing Resistance: After coating the clear coat paint onto the base     coat paint to a fixed film thickness (40 μm) using a weton-wet system,     the sample was baked for 90 minutes at 160° C. and the state of        yellowing of the paint film was observed visually.                            ◯: Hardly any yellowing of the paint film to be seen              X: Pronounced yellowing of the paint film                                     *5 Accelerated Weather Resistance: The gloss, color change and staining o     the paint film were assessed visually after testing samples for 3,000         hours with a Sunshine Carbon Arc Lamp (JIS K5400 (1990) 9.8.1). The           evaluation was made with the standards indicated below.                       ◯: Virtually no change to be seen in the paint film.              X: Water staining and color changes seen on the paint surface, and a          marked lowering of the gloss.                                            

It is clear from the results shown in Table 3 that the paint films ofExamples 1 to 5 all had excellent scratching resistance, acidresistance, hardness, yellowing resistance and weather resistance.

On the other hand, no hydroxyl group containing vinyl based monomerwhich could be represented by the aforementioned general formula (1) wasused in Comparative Example 1 and so the scratching resistance was poor.

Furthermore, a blocked isocyanate was used for the hardening agent inComparative Example 2 and so the yellowing resistance was poor.

What is claimed is:
 1. A heat-hardenable paint composition comprising(A)a vinyl based copolymer having a hydroxyl group value from 20 to 200 mgKOH/g, and comprisingfrom 5 to 70 wt % hydroxyl group containing vinylbased monomer (a-1) of the formula (1) ##STR4## wherein x¹, x² and x³each independently represent a hydrogen atom or a methyl group, j is aninteger from 0 to 2, m is an integer of from 3 to 5, n is an integer offrom 1 to 5, and from 95 to 30 wt % other vinyl based monomer (a-2), and(B) 1,3,5-triazine-2,4,6-triscarbamic acid ester of the formula

    C.sub.3 N.sub.3 (NHCOOR).sub.3

or an oligomer thereof, wherein R may be the same or different and isselected from the group consisting of an alkyl group of from 1 to 20carbon atoms, an aryl group of from 6 to 20 carbon atoms, an aralkylgroup which has from 7 to 20 carbon atoms, and mixtures thereof,whereinthe mol ratio of hydroxyl groups originating from (A) component: NHCOORgroups originating from (B) component in the composition is from 1:3 to3:1.
 2. A heat-hardenable paint composition, comprising(C) a vinyl basedcopolymer having a hydroxyl group value from 20 to 200 mg KOH/g, andcomprisingfrom 5 to 70 wt % structural units (c-1) of formula: ##STR5##wherein x¹, x² and x³ are each independently hydrogen or a methyl group,j is an integer of from 0 to 2, m is an integer of from 3 to 5, n is aninteger of from 1 to 5, from 95 to 30 wt % other structural units (c-2)derived from vinyl based monomer, and (B)1,3,5-triazine-2,4,6-triscarbamic acid ester of the formula

    C.sub.3 N.sub.3 (NHCOOR).sub.3

or an oligomer thereof, wherein R may be the same or different and isselected from the group consisting of an alkyl group of from 1 to 20carbon atoms, an aryl group of from 6 to 20 carbon atoms, an aralkylgroup which has from 7 to 20 carbon atoms, and mixtures thereof,whereinthe mol ratio of hydroxyl groups originating from (C) component: NHCOORgroups originating from (B) component in the composition is from 1:3 to3:1.